Cation Permeability of Voltage-Gated Hair Cell Ca2+ Channels of the Vertebrate Labyrinth

Some hearing, vestibular, and vision disorders are imputable to voltage-gated Ca²⁺ channels of the sensory cells. These channels convey a large Ca²⁺ influx despite extracellular Na⁺ being 70-fold more concentrated than Ca²⁺; such high selectivity is lost in low Ca²⁺, and Na⁺ can permeate. Since the permeation properties and molecular identity of sensory Ca²⁺ channels are debated, in this paper, we examine the Na⁺ current flowing through the L- and R-type Ca²⁺ channels of labyrinth hair cells. Ion currents and cytosolic free Ca²⁺ concentrations were simultaneously monitored in whole-cell recording synchronous to fast fluorescence imaging. L-type and R-type channels were present with different densities at selected sites. In 10 nM Ca²⁺, the activation and deactivation time constants of the L-type Na⁺ current were accelerated and its maximal amplitude increased by 6-fold compared to physiological Ca²⁺. The deactivation of the R-type Na⁺ current was not accelerated, and its current amplitude increased by 2.3-fold in low Ca²⁺; moreover, it was partially blocked by nifedipine in a voltage- and time-dependent manner. In conclusion, L channel gating is affected by the ion species permeating the channel, and its selectivity filter binds Ca²⁺ more strongly than that of R channel; furthermore, external Ca²⁺ prevents nifedipine from perturbing the R selectivity filter.     

基于谐波电流快速检测方法的并联型有源滤波器

在对现有并联型有源滤波器(SAPF)原理分析的基础上,提出了一种谐波电流快速检测方法.应用Matlab中Simulink电力系统模块库,对基于此谐波电流快速检测方法的SAPF进行数学建模.仿真结果表明,基于此方法的SAPF具有良好的动态抑制谐波作用.     

Frequency-Dependent Properties of the Hyperpolarization-Activated Cation Current,If, in Adult Mouse Heart Primary Pacemaker Myocytes

A number of distinct electrophysiological mechanisms that modulate the myogenic spontaneous pacemaker activity in the sinoatrial node (SAN) of the mammalian heart have been investigated extensively. There is agreement that several (3 or 4) different transmembrane ionic current changes (referred to as the voltage clock) are involved; and that the resulting net current interacts with direct and indirect effects of changes in intracellular Ca²⁺ (the calcium clock). However, significant uncertainties, and important knowledge gaps, remain concerning the functional roles in SAN spontaneous pacing of many of the individual ion channel- or exchanger-mediated transmembrane current changes. We report results from patch clamp studies and mathematical modeling of the hyperpolarization-activated current, I_f, in the generation/modulation of the diastolic depolarization, or pacemaker potential, produced by individual myocytes that were enzymatically isolated from the adult mouse sinoatrial node (SAN). Amphotericin-mediated patch microelectrode recordings at 35 °C were made under control conditions and in the presence of 5 or 10 nM isoproterenol (ISO). These sets of results were complemented and integrated with mathematical modeling of the current changes that take place in the range of membrane potentials (−70 to −50 mV), which corresponds to the ‘pacemaker depolarization’ in the adult mouse SAN. Our results reveal a very small, but functionally important, approximately steady-state or time-independent current generated by residual activation of I_f channels that are expressed in these pacemaker myocytes. Recordings of the pacemaker depolarization and action potential, combined with measurements of changes in I_f, and the well-known increases in the L-type Ca²⁺ current, I_CaL, demonstrated that I_CaL activation, is essential for myogenic pacing. Moreover, after being enhanced (approximately 3-fold) by 5 or 10 nM ISO, I_CaL contributes significantly to the positive chronotropic effect. Our mathematical model has been developed in an attempt to better understand the underlying mechanisms for the pacemaker depolarization and action potential in adult mouse SAN myocytes. After being updated with our new experimental data describing I_f, our simulations reveal a novel functional component of I_f in adult mouse SAN. Computational work carried out with this model also confirms that in the presence of ISO the residual activation of I_f and opening of I_CaL channels combine to generate a net current change during the slow diastolic depolarization phase that is essential for the observed accelerated pacemaking rate of these SAN myocytes.     

烧碱工艺路线的选择与电流密度的确定

通过对隔膜法和离子膜法两种工艺路线投资和技术经济方面的分析对比,对两种工艺提出看法。通过建立简单的数学模型,为金属阳极隔膜电解槽和离子膜电槽的最佳经济电流密度的确定提供参考依据。     

Li_2O·MnO_2-Ag-YSZ氧泵型反应器中NEMCA效应的研究

本文对Ｌｉ２Ｏ·ＭｎＯ２－Ａｇ－ＹＳＺ氧泵型催化膜反应器中甲烷氧化偶联反应的ＮＥＭＣＡ效应进行了研究。考察了稳态电流和反应温度对ＮＥＭＣＡ效应的影响,考察了反应气中甲烷含量、反应温度对发生ＮＥＭＣＡ效应时的交换电流密度的影响,比较了传递体系和联合体系的交换电流密度与活性过电位的关系。结果表明：高甲烷含量、低反应温度和反应气中引入极少量的Ｏ２,可降低三相界面的交换电流密度,有利于ＮＥＭＣＡ效应的发生     

2万t/a离子膜烧碱装置运行情况

介绍了广州昊天化学集团有限公司2万t/a烧碱扩产项目实施及运行情况,离子膜电流效率急剧下降的问题经换膜得到解决。     

脉冲电流和脉冲磁场作用下LY12铝合金凝固组织的比较

以我们所做的实验结果为根据 ,发现脉冲磁场对 L Y12铝合金凝固组织的细化效果要好于脉冲电流 ,并比较了脉冲电流和脉冲磁场这两种新颖的脉冲电磁场技术对其凝固组织的细化和机理差别、工作原理和特点 ,指出了应用前景     

Adapting an ultrasonic image threshold method to eddy current images and defining a validation domain of the thresholding method

This paper presents a generalization to eddy current images of a thresholding method developed for ultrasonic imaging. It is also shown how to improve the thresholding strength through the definition of a cooperation rule between two threshold assessment measures. This rule is also used to reduce time of calculus. These measures are calculated from the image cooccurrence matrix. The aim is to build a thresholding method that gives a threshold value but also an indicator which allows the operator to know if the methodology applies to the processed image. Examples of results are presented.     

脉冲电流对金属材料塑性变形和组织结构与性能的影响

脉冲电流对金属材料的塑性变形、组织结构和力学性能有显著影响。利用高强脉冲电流可显著改善金属材料的加工性能及力学性能；能改变疲劳损伤金属材料的位错组态，提高其疲劳寿命；能促进一些冷变形合金的再结晶过程；能减少合金凝固组织中的缩孔、缩松。由于利用脉冲电流可改善金属材料加工性能及力学性能，并促进组织结构转变，因此在金属材料加工和组织结构调整等领域有着广阔的应用前景。     

大电流直流正接MAG焊接工艺的研究

采用试验手段确定了适用于直流正接MAG焊的保护气体,分析了不同焊接电流条件下的直流正接MAG焊电弧形态、熔滴过渡行为和焊缝成形特点,最后给出了大电流直流正接MAG焊的最佳工艺区间。